src/HOL/UNITY/Union.thy
1998-08-13 paulson 1998-08-13 Constrains, Stable, Invariant...more of the substitution axiom, but Union does not work well with them
1998-08-05 paulson 1998-08-05 Null program and a few new results
1998-08-05 paulson 1998-08-05 Union primitives and examples